The present invention relates, in general, to power devices for securing rotatable fastener elements such as screws, nuts, etc. and more particularly to fluid powered devices. In general such devices engage in multiple rotation of a fastener holder, such as a socket wrench and the device rotates until a "stall" point when the torque applied to the device is equal to the resistance of the fastener to further rotation. This point is generally somewhat less than the final desired rotation required to send the fastener element "home". In other applications it is desirable to rotate the fastening element to a selected final torque. In either case an initial multi rotational sequence is required followed by a final rotation to the desired torque or "home" position. In virtually, all cases the apparatus can be designed so that the difference between the "stall" position and the final position or final torque is less than one full rotation of the shaft.
When motorized rotation devices are employed another factor also affecting the seating of the fastener device is the inertial reservoir provided by the momentum generated as a function of the rotational speed at which the equipment operates and the mass of the rotating members thus resulting in a reservoir of energy to be applied at the end of the rotational sequence. The problem is that the inertial energy the resistance to rotation varies from fastening element to fastening element. Where a sequence of elements is to be secured to a selected torque or position it becomes necessary to also provide a final adjustment of the torque or position.
The prior art includes U.S. Pat. No. 2,893,278 which provides some similar aspects of the present invention. However, the present invention is distinguishable, and an improvement over the features of the teachings of the U.S. Pat. No. 2,983,278, specifically, because the reference teaches a motor which is not part of an overall fluid power loop as in the present case and is not operated in response to characteristic changes within the loop. On the contrary, motor for example an electric motor is taught by the reference to turns shaft to a preselected position at which time the motor stalls out and a second driving mechanism, a fluid actuator is engaged to drive the fastening element to the final "home" position or final torque.
Likewise U.S. Pat. No. 3,952,176 teaches an arrangement where tightening of the fastener element is accomplished by rotational element and where the final torque adjustment is accomplished by the engagement of a rack and pinion device which moves to finally secure the element to the final torque.
The present invention is likewise distinguishable over this reference inasmuch as in the present invention both of the actuator elements are rotatary devices, connected to the same shaft in generally coaxial relationship and operable from the same power loops.
Additional prior art arrangements are shown in U.S. Pat. No. 3,587,365, U.S. Pat. No. 3,834,467, and U.S. Pat. No. 3,845,673.
In summary, no prior art arrangement is known which provides the advantagous fluid power circuit provided by the present invention to secure a rotatable fastener to a selected position or to a selected torque in the manner described and claimed hereinafter.